1. Field of the Invention
The present invention relates to a processing method and to a processing apparatus in which a thick peripheral reinforcing portion of a wafer (for example, a semiconductor wafer), which is formed around a region of the wafer having devices (for example, semiconductor chips) formed thereon, is removed from the wafer and the wafer is transferred to a next process.
2. Description of Related Art
In general, semiconductor chips, which are used in various electronic apparatuses, are produced by the following method. That is, grid-like rectangular regions are defined by predetermined division lines on a disc-shaped semiconductor wafer, and electronic circuits are formed on surfaces of the rectangular regions. Next, a rear surface of the wafer is ground so as to be thinned. The wafer is divided along the predetermined division lines. As a result, semiconductor chips are produced. In recent years, electronic apparatuses have been greatly improved in compactness and thinness. In accordance with this, semiconductor chips are required to be even thinner, and semiconductor wafers are required to be thinner than previously.
When a semiconductor wafer is thinned, the rigidity of the semiconductor wafer is decreased. Due to this, it is difficult to handle the semiconductor wafer after the thinning, and cracking easily occurs in the semiconductor wafer. In order to solve these problems caused by the thinning, only the rear surface of circular device region, which has semiconductor chips formed on the surface, is ground so as to be thinned, and a ring-shaped peripheral extra region around the device region is thereby formed as a relatively thick reinforcing portion. In this case, since the rear surface is ground, the thick peripheral reinforcing portion projects on the rear surface and the entire semiconductor wafer has a recessed shape in cross section. The technique, in which only the peripheral portion is allowed to be thick, has been disclosed in Japanese Unexamined Patent Applications Publication Nos. 2004-281551 and 2005-123425.
In conventional techniques, in order to easily handle a thinned semiconductor wafer, a protective tape was applied to a surface of the semiconductor wafer so as to provide rigidity thereto. However, when a metal film composed of gold is provided by a method (for example, deposition or sputtering) on a rear surface of the semiconductor wafer after thinning, the protective tape has insufficient heat-resistance, so that the processing temperature needed to be lower. Due to this, processing is more time-consuming in this case than in normal cases. In contrast, in the above rigidity improvement technique by formation of a peripheral reinforcing portion, since the rigidity is maintained even when the protective tape is peeled from the semiconductor wafer after the thinning, the above rigidity improvement technique by formation of a peripheral reinforcing portion is superior in that deposition or sputtering can be performed without consideration of heat effects.
In the above manner, the semiconductor wafer is finally divided into plural semiconductor chips. In this case, a typical dividing method for semiconductor wafer is a method in which a semiconductor wafer, which is chucked and held on a vacuum chuck-type table, is cut off by a cutting blade. In this method, a rear surface of the semiconductor wafer is applied to and supported by an adhesive surface of a dicing tape which is provided to a ring-shaped dicing frame, and the dicing tape is chucked on the chuck table. As a result, the semiconductor wafer is supported by the chuck table.
In this case, if the semiconductor wafer has a typical plate shape, the entire rear surface of the semiconductor wafer closely contacts the chuck table, so that the semiconductor wafer is stably held. However, when the semiconductor wafer has the above peripheral reinforcing portion, it is difficult to stably hold the semiconductor wafer. In order to solve this problem, it was conceived that the chuck table could be modified to have a shape to which the recessed rear surface of the semiconductor wafer having the above peripheral reinforcing portion is fitted. However, since this modification of the chuck table is not practical, the above peripheral reinforcing portion of the semiconductor wafer is removed, so that the entire semiconductor wafer is processed to have a plate shape.
In order to remove a peripheral reinforcing portion, for example, there are the following methods. In one method, a cutting blade cuts a boundary between a peripheral reinforcing portion and a device region, and it cuts off the peripheral reinforcing portion. In the other method, a peripheral reinforcing portion is ground by a grinding stone or a cutting blade. The wafer after the removal of the peripheral reinforcing portion is transferred to a process in which the wafer is cut off and divided into semiconductor chips in the above manner. However, in this case, since the peripheral reinforcing portion of the wafer is removed, the rigidity of the wafer is low and damage (for example, cracking) easily occurs in the wafer. Due to this, when the wafer is transferred from the removal process for removing the peripheral reinforcing portion to the dividing process for dividing of wafer into semiconductor chips, a method for reliably transferring of the wafer without damage occurring in the wafer is required.